Rock Splitting Test, Uniaxial Compression And Direct Tensile Deformation Behavior Of The Experimental Study

It is well known that rocks bear compressive stress rather than tensile stress in most cases. As a consequence, the deformation parameters and the constitutive models of rocks deduct from only compressive tests in the practical rock engineering. However, some researches have shown that Young's modulus in direct tension, ET, is much smaller than the modulus in compression, EC, for some rocks. For such rocks, large error may be produced if their constitutive models and the deformation parameters such as Young's modulus and Poisson's ratio are obtained from only compressive tests, and the larger difference between EC and ET, the greater error would be produced.Unfortunately, most investigations on the deformation behavior of rock are conducted from only compression so far. The constitutive models of rocks and failure criterion are incomplete under tension and compression. Actually, only bimodularity is recommended to constitutive models of rocks in tensile and compressive tests. More researches are then needed to investigate the deformation behavior of rocks under both tension and compression.In the research works involved in this paper, Uniaxia compression, Direct tension,Brazilian test in one-way and vary rang cyclic loading tests with different loading routes and stress levels were porformed with three rock types. It was developed by Kunming University of Science and Technology that the testing apparatus can conduct both compression and direct tension tests with the same rock sample. Furthermore,the deformation behavior with different loading routes,stress levels and different types of rock is studied.The damaging from of the rock is described and analyzed from the angle of damage theory,which further explains the failure mechanism and development process of fatigue under uniaxia loading.The research indicates:for the three types rock in this test,, Young's modulus in direct tension, ETA, are nearly equal to the modulus in compression, ECA, for two rock types. For another type of rock, Young's modulus in tension is much smaller than the modulus in compression. Both types showed different deformation characteristics in uniaxial compression and tension cyclic loadings. The rocks, whose ET is nearly equal to EC, can be basically regarded as elastic material. For the rocks of which ET is much less than EC, the deformation in compression is generally elastic, while the deformation in tension is prominent plastic.All deformation of material under cyclic loading has obvious hysteresis chdracteristics, and forms stress-strain hysteresis curve. The plastic-loop gradually changes with the increase of stress levels. the cyclic loading has a smaller impact on deformation characteristics and mechanical parameters of rock, the outsourcing network load line of rock in cyclic loading process is almost monotonous to curves stress-strain in uniaxia loading. The loading and unloading path of rock ample does not fully coincide, and there does not exist one-to-one relationship between Stress and strain curve,which indicates linear deformation of the rock sample does not mean the elastic deformation.The development of fissures also influence on the compression and tensile deformation in the process of splitting cyclic loading,which is much greater than tensile than compression. When the fissures do not make rock damage,the deformation curve under two states can return to the trend of development before fissures after they experience similar abnormal "trajectory", and Young's modulus and other deformation parameters are not affected.Young's modulu of rock under compression and tensile under the process of loading showed the opposite trend of development with improvement the load stress level under splitting tensile cyclic loading. Compression load Young's modulus increased slightly, while tensile load Young's modulus reduced. Under unloading process, Young's modulus in both states is similar to changes with loading. When the cyclic loading stress reach the previous cyclic loading the maximum stress, part the of rocks have shown varying degrees plastic deformation in state of tension and compression, which outsourcing network lines of cyclic loading deformation curve are not well connected,and show scattered irregular-shaped. This phenomenon is particularly prominent when rock produce some larger fissures, which shows that generation and development of fissures have close relationship with the horizontal deformation.In the cyclic loading process beteen tension and compression, Young's of most rocks changes little from the compression tests (tensile) to the tensile (compression) phase. However, the changes of Poisson's ratio in compression and that in tensin are much complicated than that of Young's. The main reason of which lies in:regardless of compression or stretching conditions, the change of Poisson's ratio is mainly related with the rock formation and expansion of crack in rock.The compression and tension are not quite different courses.The deformation curve of unloading in compression jion continuously together with that of loading in tension in thecyclic loading process beteen tension and compression,which two stages deformation curves are continuous and smooth transition. The deformation curve of compression curve jions smoothly with that of tensile at the origin connection in Brazilian splitting cyclic experiment.There happens simultaneity to distribute and dissipate of energy from outside in rock in damage and failure process of rock. The quantity and form of fissures of rock depend on response of external loading and energy distribution mechanism. The expansion of its micro-mechanism of deformation on the macro performance is the three stages of the development including initial stage,stabilization phase and accelerated phase.